Multi-laser system and method for cutting and post-cut processing hard dielectric materials

ABSTRACT

Laser processing of hard dielectric materials may include cutting a part from a hard dielectric material using a continuous wave laser operating in a quasi-continuous wave (QCW) mode to emit consecutive laser light pulses in a wavelength range of about 1060 nm to 1070 nm. Cutting using a QCW laser may be performed with a lower duty cycle (e.g., between about 1% and 15%) and in an inert gas atmosphere such as nitrogen, argon or helium. Laser processing of hard dielectric materials may further include post-cut processing the cut edges of the part cut from the dielectric material, for example, by beveling and/or polishing the edges to reduce edge defects. The post-cut processing may be performed using a laser beam with different laser parameters than the beam used for cutting, for example, by using a shorter wavelength (e.g., 193 nm excimer laser) and/or a shorter pulse width (e.g., picosecond laser).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of co-pending U.S. patentapplication Ser. No. 14/838,809 filed Aug. 28, 2015, which claims thebenefit of U.S. Provisional Patent Application Ser. No. 62/043,363 filedAug. 28, 2014, which is fully incorporated herein by reference. Thepresent application is related to International Application No.PCT/US14/19460 filed Feb. 28, 2014 (Attorney Docket No. IPGP004PCT)entitled LASER SYSTEM AND METHOD OF USING SAME FOR PROCESSING SAPPHIREand U.S. Provisional Patent Application Ser. No. 61/945,911 filed Feb.28, 2014 (Attorney Docket No. IPGM006P) entitled MULTIPLE-BEAM LASERPROCESSING USING MULTIPLE LASER BEAMS WITH DISTINCT WAVELENGTHS AND/ORPULSE DURATIONS, both of which are fully incorporated herein byreference.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present disclosure relates to processing hard dielectric materialsusing lasers, and more particularly, relates to a multi-laser system andmethod for cutting and post-cut processing hard dielectric materialssuch as ceramics.

Background Art Discussion

Hard dielectric materials, such as sapphire (Al₂O₃), toughened glass(e.g., GORILLA® glass), and other ceramics, may be used for manyindustrial applications such as optical windows, hard materialspreventing abrasion, and buffer materials for a semiconductor emittingdevice, and the like. Conventional mechanical methods for treating orprocessing sapphire and other such materials include diamond scribingand blade dicing; however, these methods often lead to breaking thesubstrate, which lowers production yields.

Laser processing methods have been used in an effort to increaseefficiency because they provide a noncontact process that is moreefficient for high volume production. The laser scribed cutting depthmay also be controlled to reduce stress on the wafer during the breakprocess, and laser scribing facilitates precise positioning of scribes.Thus, laser processing has overall advantages of increased throughput,low cost, ease of use, and high yields compared to traditionalmechanical methods.

Certain materials, however, present challenges when processing usinglasers. The bandgap of sapphire, for example, is approximately 8 eV, andunder normal low intensity illumination, sapphire is opticallytransparent from 5000 nm to about 300 nm. Therefore, conventional laserprocessing of sapphire has used lasers that are more likely to beabsorbed in sapphire, such as DUV and UV lasers operating in awavelength range between about 157 and about 355 nm.

Laser processing of sapphire has also been performed using ultrafastlasers (e.g., picosecond and shorter pulse widths) and/or Q-switchedpulse lasers with nanosecond pulse widths. Such lasers may be used toemit pulses with high peak power capable of ablating sapphire.Picosecond lasers may also be used to focus inside a sapphire substrateforming cracks within the substrate without affecting the top and bottomsurfaces. The cut parts may then be mechanically separated from thesubstrate after the cracks are formed.

The existing techniques used for laser processing of sapphire discussedabove also suffer from other drawbacks. In particular, the cost ofpulsed lasers is high and the multi-step process of forming cracks andseparating parts is time consuming and cost inefficient. Also, thewavelengths used in UV cutting require the use of crystals, which mayhave a short useful life and may present issues with the maintenance ofthese lasers.

Cutting hard dielectric materials also presents challenges because ofthe defects and imperfections that might form in the material aftercutting. Hard dielectric materials including crystalline and amorphousceramics have a tendency to fail in tension before they fail incompression. Stress concentrations at the cut edges, for example, maylead to crack propagation throughout the material. These materials maybe more susceptible to these defects and imperfections when certaintypes of lasers are used to perform the cutting. Sometimes the lasersthat perform the cutting most efficiently (e.g., at a lower cost andhigher speeds) may cause edge defects such as chipping, cracking, andinduced stress concentrations proximate the cut edges.

Accordingly, a need exists for a system and method of efficiently lasercutting hard dielectric materials at increased speeds in atime-effective and a cost-effective manner while also reducing edgedefects.

SUMMARY OF THE DISCLOSURE

Consistent with an embodiment, a method is provided for laser cuttingand post-cut processing a part from a hard dielectric material. Themethod includes: cutting at least one part from a hard dielectricmaterial using at least a first laser beam, wherein the first laser beamis emitted from a continuous wave laser operating in a quasi-continuouswave (“QCW”) mode so as to emit consecutive pulses of laser light at awavelength ranging between about 1060 nm and about 1070 nm; and post-cutprocessing cut edges of the at least one part using at least a secondlaser beam to bevel and/or polish the cut edges of the at least one partsuch that edge defects are reduced.

Consistent with another embodiment, a multi-laser system includes afirst laser system for cutting at least one part from a hard dielectricmaterial using at least a first laser beam and a second laser system forpost-cut processing cut edges of the at least one part using at least asecond laser beam to bevel and/or polish the cut edges of the at leastone part such that edge defects are reduced. The first laser systemincludes a continuous wave laser operating in a quasi-continuous wave(“QCW”) mode so as to emit consecutive pulses of laser light at awavelength ranging between about 1060 nm and about 1070 nm. Themulti-laser system also includes at least one motion stage forsupporting the hard dielectric material and the cut part and for movingthe hard dielectric material and the cut part relative to the firstlaser system and the second laser system, respectively. The multi-lasersystem further includes a control system configured to control the firstlaser system, the second laser system and the at least one motion stage.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages will be better understood byreading the following detailed description, taken together with thedrawings wherein:

FIG. 1 is a schematic diagram of a laser processing system for cutting ahard dielectric material using a quasi-continuous wave (QCW) lasersystem, consistent with an embodiment of the present disclosure.

FIG. 2 is a schematic diagram of a multiple-beam laser processingsystem, consistent with another embodiment of the present disclosure.

FIG. 3 is a schematic diagram of a multiple-beam laser processingsystem, consistent with a further embodiment of the present disclosure.

FIGS. 4A-4C illustrate a method for polishing a cut edge of a part cutfrom a hard dielectric material, consistent with an embodiment of thepresent disclosure.

FIGS. 5A-5C illustrate a method for polishing a beveled cut edge of apart cut from a hard dielectric material, consistent with anotherembodiment of the present disclosure.

FIGS. 6A-6D illustrate a method for beveling a cut edge of a part cutfrom a hard dielectric material by laser milling with a perpendicularlaser beam, consistent with an embodiment of the present disclosure.

FIGS. 7A-7D illustrate a method for beveling a cut edge of a part cutfrom a hard dielectric material by laser milling with an angled laserbeam, consistent with another embodiment of the present disclosure.

FIGS. 8A and 8B illustrate a method for beveling a cut edge of a partcut from a hard dielectric material by laser cutting, consistent with afurther embodiment of the present disclosure.

FIG. 9A is a perspective view of an angled laser beam aligned withdifferent axes relative to a part, consistent with an embodiment of thepresent disclosure.

FIGS. 9B and 9C illustrate a method for beveling an edge of a part bymoving the cut part with coordinated motion relative to continuouslychange the angle of the angled laser beam to produce a rounded bevel,consistent with an embodiment of the present disclosure.

FIGS. 10A and 10B illustrate another method for beveling an edge of apart by moving the part away from a horizontal axis relative to the beamto continuously change the angle of the angled beam to produce a roundedbevel, consistent with another embodiment of the present disclosure.

FIGS. 11A and 11B are perspective views of an angled laser beam orientedrelative to a circular part with the angled beam aligned at differentangles relative to the radius of the circular part to provide differentbevel angles, consistent with an embodiment of the present disclosure.

FIGS. 12A and 12B illustrate coordinated motion of a circular partrelative to an angled beam for beveling an edge of the circular part,consistent with embodiments of the present disclosure.

FIG. 13 is a schematic diagram of a circular part illustratingparameters for providing coordinated motion for beveling an edge of thecircular part, consistent with an embodiment of the present disclosure.

FIG. 14 is perspective view of a circular part with a laser beam forminga straight beveled edge.

FIG. 15 is a perspective view of a circular part with a rounded bevelededge.

DETAILED DESCRIPTION

Laser processing of hard dielectric materials, consistent withembodiments of the present disclosure, may include cutting a part from ahard dielectric material using a continuous wave laser operating in aquasi-continuous wave (QCW) mode to emit consecutive laser light pulsesin a wavelength range of about 1060 nm to 1070 nm (hereinafter “QCWlaser”). Cutting using a QCW laser may be performed with a lower dutycycle (e.g., between about 1% and 15%) and in an inert gas atmospheresuch as nitrogen, argon or helium. Laser processing of hard dielectricmaterials may further include post-cut processing the cut edges of thepart cut from the dielectric material, for example, by beveling and/orpolishing the edges to reduce edge defects. The post-cut processing maybe performed using a laser beam with different laser parameters than thebeam used for cutting, for example, by using a shorter wavelength (e.g.,193 nm excimer laser) and/or a shorter pulse width (e.g., a picosecondlaser).

As used herein, “hard dielectric materials” refers to dielectricmaterials including ceramics having a hardness greater than 5 on theMohs scale. Examples of hard dielectric materials include, withoutlimitation, sapphire and GORILLA® glass. Sapphire is a single crystalform of alumina (Al₂O₃), which is transparent to light wavelengthsbetween about 170 nm and 5300 nm, five (5) times stronger than glass,and nine (9) on the Mohs scale of hardness. Sapphire is also a goodelectrical insulator and has a high thermal conductivity. Sapphire maybe particularly advantageous in manufacturing of blue and green lightemitting diodes (“LEDs”). Sapphire also has potential for replacing theexisting glass covering the screen for a mobile device including, butnot limited to, telephones, cameras, computers and the like. Thus, thelaser processing systems and methods described herein may be used to cutsapphire substrates to a desired shape for use in manufacturing photonicdevices, screens and other products incorporating sapphire.

As used herein, “edge defect” refers to chipping, cracking, stressconcentrations and/or other defects having a tendency to cause crackpropagation in hard dielectric material, which are located at a cut edgeof a part. As used herein, “bevel” and “beveling” refer to the use of alaser to remove material at an edge of a part such that at least aportion of the edge is no longer perpendicular to a surface of the partand includes chamfering. As used herein, “polish” and “polishing” referto the use of a laser to ablate and/or melt material on an edge of apart such that the edge becomes smoother without substantially changingthe angle of the edge relative to the surface of the part.

As used herein, “wavelength” refers to an approximate emissionwavelength of a laser and may encompass a band or range of wavelengthsaround the stated wavelength. As used herein, “ultraviolet (UV) range”refers to a spectral range of 10 nm to 380 nm, “visible range” refers toa spectral range of 380 nm to 700 nm, “green range” refers to a range ator near 532 nm, and “infra-red range” refers to a spectral range of 700nm to 10.6 μm. As used herein, “ultrafast laser” refers to a laser thatemits laser pulses with a duration or pulse width of less than 1nanosecond and including durations of picoseconds and femtoseconds and“picosecond laser” refers to a laser that emits laser pulses with aduration or pulse width between 1 picosecond and 1 nanosecond. As usedherein, “absorption center” refers to a location in a non-absorptivematerial where the properties of the material have been modified (e.g.,craters, roughening, optical damage, internal material defects, colorcenters, bulk material property changes, or increased temperature) suchthat light is more likely to be absorbed as compared to an unmodifiedregion of the material.

Referring to FIG. 1, an embodiment of a laser processing system 100 isdescribed for processing a workpiece 102, such as a sapphire substrate,using a focused laser beam. The workpiece 102 may also be made fromother large bandgap and/or transparent materials including, withoutlimitation, aluminum diamond, gallium nitride, silicon carbide, zincselenide, silicon, silicon nitride, aluminum nitride, gallium nitride onsapphire, and glass (e.g., fused quartz or silica). Although the exampleembodiments described herein mostly relate to laser treatment orprocessing of sapphire or other hard dielectric materials, at least someof these other large bandgap materials can be successfully treated withthe disclosed laser processing systems.

In the illustrated embodiment, the laser processing system 100 includesa QCW single mode (SM) fiber laser 110 emitting a single mode,divergence limited laser beam 111 from the downstream end of aprocessing passive fiber 112. The QCW fiber laser 110 may range in powerfrom 500 W to 50 kW and may have a monolithic, entirely solid state,fiber-to-fiber design that does not require mirrors or optics to alignor adjust. The QCW fiber laser 10 may also be modular, built frommultiple laser units, each one generating hundreds of watts of outputpower. This also allows the laser system to incorporate reserve modulesand power margins. The QCW SM fiber laser may include, for example, aQCW SM ytterbium fiber laser with an emission wavelength of about 1070nm, such as the QCW series available from IPG Photonics Corporation. Inother embodiments, the laser may include a fiber disc laser or a rodlaser such as a Nd: YAG laser. Multi-mode lasers may also be used.

The laser processing system 100 also includes a collimator 130 tocollimate the beam 111 and a beam bender or reflector 132 to direct thebeam 111 to a focus lens 140. The focus lens 140 may focus the beam 111to a relatively small spot size, for example, in a range of about 14-30μm. Alternatively or additionally, other optics may also be used formodifying and/or directing the laser light to the desired location. Suchoptics may include, without limitation, beam expanders, beamcollimators, beam shaping lenses, reflectors, masks, beamsplitters andscanners (e.g., a galvanometer).

The laser processing system 100 further includes a laser head includinga nozzle 160 coupled to a gas delivery system 162. The gas deliverysystem 162 may provide a stream of inert gas, such as nitrogen, argon orhelium, to the nozzle 160 close to the work area when processing theworkpiece 102. The gas may be delivered with a pressure in a range ofabout 100 to 300 psi. The presence of the inert atmosphere improves theefficiency of the laser processing.

The laser processing system 100 further includes a translation stage 170configured to impart a translational motion to the workpiece 102 in oneor more axes or dimensions, thereby allowing the workpiece 102 to moverelative to the focused laser beam. The translation stage 170 may beoperated manually or may receive commands from a controller 172.Alternatively, the laser 110 may be moved and displaced relative to theworkpiece 102 to be processed. The controller 172 includes processingcircuitry, such as a central processing unit (“CPU”), to communicatewith translation stage 170.

The QWC SM fiber laser 110 includes a pump source 114 operable to beswitched on for time intervals having a duration long enough to operatethe laser as close to its steady state as possible, i.e. the laser isoptically in the state of continuous-wave operation, also referred to asa quasi-continuous wave (QCW) mode. The controller 172 may be used tocontrol the pump source 114. The percentage of time the laser isswitched on, i.e., the duty cycle, is selected to reduce the heating andheat related problems. The controller 172 may control the pump source114, for example, to have a duty cycle in a range of about 1% to 15%.Therefore, the QCW SM fiber laser 110 operating in the QCW mode may havehigher output peak powers and lower average powers. For cutting harddielectric materials, the pulse width or duration may range from 10 μsto 600 μs depending upon the thickness of the cut with the shorter pulsedurations being possible for sapphire less than 400 microns thick andlonger pulse durations for increased thicknesses over 1 mm.

Various machining techniques may improve cutting of hard dielectricmaterials using the laser processing system 100 described above. Thelaser processing system 100, for example, may perform substantiallyconstant speed machining without stopping to maintain the cut andminimize cracks and/or constant pulse spacing to maintain asubstantially constant average power applied to the workpiece 102. Oncea cut is initiated in the workpiece 102 made of sapphire, for example,the properties of the molten sapphire change dramatically (e.g.,reflectively decreases) and maintaining a substantially constant speedand/or average power may avoid cutting inconsistencies caused by drasticvariations in temperature. If the cutting speed increases or decreases,the laser parameters may be adjusted in real time to maintain asubstantially constant average power. Maintaining substantially constantaverage power may also improve cutting in highly stressed sapphire.Stress may also be relieved in highly stressed sapphire by drillingstress relief holes in the sapphire prior to cutting.

In other embodiments, different process parameters (e.g., cutting speedand repetition rate) may be used per cutting axis for different sapphiretypes such as A-plane sapphire and C-plane sapphire. Because the C-planeis the base of the hexagonal sapphire crystal, cutting normal to theC-plane may demonstrate symmetry in cut quality.

In further embodiments, the focus placement of the laser beam may beoptimized based on the material thickness. For a 1 mm sapphireworkpiece, for example, the range of focus of the laser beam may be from250 μm inside the material (i.e., −250 μm) up to 1 mm above the material(i.e., +1000 μm) in order to obtain an optimum quality and partseparation. For a 0.4 mm thickness, the range may be from −200 μm to+200 μm.

In one example, a sapphire substrate with a thickness of 0.7 mm wasprocessed using the following process and laser parameters: a Ytterbium(Yb) single mode laser; 1070 nm wavelength; 14 μm fiber core diameter;60 mm collimating distance; 123 mm focal length; 28.7 μm spot size; 900W peak power; 87.5 μs pulse duration; 400 Hz pulse frequency; 78.7 mJpulse energy; argon or nitrogen assist gas at 250 psi; 0.5 mm nozzlestand off; 1.5 mm nozzle orifice; and 8.46 mm/s cutting speed.

In another example, sample sapphire substrates of different thicknesses(e.g., 0.015 in. and 0.040 in.) were processed with different processingoperations (e.g., scribing, cutting, and drilling) using a Yb-doped QCWSM fiber laser at different duty cycles, pulse frequencies and speeds.The following Table I illustrates the parameters used for theseprocessing operations:

TABLE I Speed Sapphire (inches per thickness Frequency Duty minuteAssist (inches) Process Power (W) (Hz) Cycle (%) (“ipm”)) gas 0.015″Scribing 285 3500 20 420 30 psi N₂ 0.015″ Cutting 285 2000 40 40 30 psiN₂ 0.015″ Drilling 285 2000 40 <10 30 psi N₂ 0.040″ Scribing 285 2500 25360 30 psi N₂ 0.040″ Scribing 285 500 30 30 30 psi N₂ 0.040″ Drilling285 2000 30 <10 30 psi N₂

In this example, scribing of the 0.015″-thick sapphire sample with alaser beam at 285 W removed about 30% of the thickness of the sample ata speed of about 420 ipm. Cutting the 0.015″-thick sapphire sample wasalso effective at a 285 W power and speed of about 40 ipm. Drillingcircular holes in the sapphire samples was successful at relatively lowspeeds. The same processing operations were also successfully performedon the 0.040″ thick wafer.

These examples illustrate that sapphire substrates can be efficientlyprocessed by a QCW SM fiber laser at a wavelength in the range of about1060-1070 nm. The single mode beam with a relatively small spot providesa high power density capable of breaking down the material. Betterprocessing appears to be possible at lower duty cycles, i.e., lowaverage powers. The peak power and average power may need to be higheras the material thickness increases, but the low duty cycle appears tobe more of a key factor than peak power.

In a further example, a high-quality cut may be achieved at 900 W, 500Hz and 3% duty cycle (i.e., average power of 27 W) with a speed of 20inches/min. In this example, the cutting speed may be doubled to 40inch/min by increasing the pulse frequency to 1000 Hz. The quality ofthe cut may deteriorate in response to scaling up the laser power. Also,the quality may improve at shorter pulse widths (e.g., 50-100microseconds), which may lead to a high-speed process. The longer pulsesalso provide high quality cuts, but increasing the duty cycle results inlonger periods of time to complete the processing.

In yet another example, sapphire substrates with a thickness betweenabout 0.4 mm and 0.7 mm were processed using the following process andlaser parameters: a Ytterbium (Yb) single mode laser; 1070 nmwavelength; 14 μm fiber core diameter; 60 mm collimating distance; 123mm focal length; 28.7 μm spot size; argon or nitrogen assist gas at 250psi; and 1.5 mm nozzle orifice. The following Table II shows the resultsof processing using the above parameters with different peak power,frequency, duty cycle, pulse width and cut speed.

TABLE II Peak Duty Pulse Power Frequency Cycle Width Cut Speed #Material (W) (Hz) (%) (ms) (Inch/min) Comments 1 0.4 mm 400 160 2.750.171 12 Very fine powdery dross. The dross polished rubs off easilyjust by wiping it. Some chipping and cracks. Less than <30 microns atrandom places. 2 0.7 mm 900 400 3.5 0.0875 16-20 Very fine powderydross. The dross unpolished rubs off easily just by wiping it. Nocracking but some chipping. Less than <40 microns at random places. 30.7 mm 750 300 3.5 0.116 12 Very fine powdery dross. The drossunpolished rubs off easily just by wiping it. No cracking but somechipping. Less than <40 microns at random places. Optics used is200Focal/120 mm collimator.

Based on the foregoing, a QCW SM laser with a wavelength in a range of1060-1070 nm can be successfully used for cutting a sapphire substratewith minimal cracks and chipping. In the above example, the 0.7 mm thicksubstrate has better cut quality. The 0.4 mm thick substrate exhibitschips along the edge of the cuts; however, the chips are generally lessthan 40 microns, which is considered to be a high quality cut as knownto one of ordinary skill. The laser processing method disclosed hereinalso appears to be sensitive to high frequencies with significantchipping occurring at higher frequencies. The quality of the cuts alsodepends on the duration of duty cycle with a lower the duty cycleimproving the cut quality. Peak power above 1600 W with a duty cycle ofup to 10% may not provide any visible advantages, but a duty cycle lowerthan 1% may deteriorate the quality of cuts. A gas pressure rangebetween 200 and 300 psi also improved the efficiency of the process inthese examples. The beam spot size is generally between about 14 and 30microns, and using a spot size lower than 14 microns generally does notsubstantially affect the quality and efficiency of the process.

In a further example, sapphire substrates with a thickness of 2.7 mmwere successfully cut using a multimode QCW laser with a 50 micron fiberwith the following parameters: 15 kW peak power; 450 W average power;0.6 ms pulse width; 100 micron spot size; 50 Hz repetition rate; 3% dutycycle; 10 ipm speed; argon gas at 100 psi; a 1.5 mm nozzle diameter; anda 1 mm standoff. The use of argon or helium as the assist gas was foundto improve cutting efficiency, possibly because of the trace Ti found insapphire.

Referring to FIG. 2, a multiple-beam laser processing system 200 mayalso be used to process sapphire or other hard dielectric materials.Multiple-beam laser processing may be performed on a sapphire substrateor workpiece 202 using both an assist laser beam 211 and a process laserbeam 221 with different characteristics (e.g., wavelengths and/or pulsedurations). The assist laser beam 211 is directed at a target location208 on or within the workpiece 202 to modify a property of the sapphire(e.g., induce damage or increase temperature) such that absorptioncenters are formed in the sapphire. The process laser beam 221 isdirected at the target location 208 and is coupled into the absorptioncenters formed in the sapphire to complete processing of the sapphire.The assist laser beam 211 and the process laser beam 221 individuallyare not capable of completely processing the sapphire workpiece buttogether (either simultaneously or sequentially) provide a synergy thatenables processing.

The illustrated embodiment of the multiple-beam laser processing system200 includes an assist laser 210 for generating the assist laser beam211 (e.g., a green laser of about 532 nm) and a process laser 220 forgenerating the process laser beam 221 (e.g., a QCW SM fiber laser ofabout 1060 to 1070 nm). The assist and process lasers 210, 220 areoptically coupled to respective beam delivery systems 212, 222 formodifying the assist and process laser beams 211, 221, respectively,before combining the beams. The multiple-beam laser processing system200 further includes a beam combiner 230, a focus lens 240, a laserprocessing head 260, and one or more reflectors or mirrors 252, 254, 256for directing the assist and process laser beams 211, 221 as a combinedlaser beam 231 to the same target location 208 on or within a workpiece202.

Although the illustrated embodiment shows the assist and process laserbeams 211, 221 being combined simultaneously, the beams 211, 221 mayalso be combined such that the beams are directed to the same targetlocation 208 at different times. Directing the laser beams 211, 221simultaneously may include any amount of overlap between the bursts orpulses of the laser beams 211, 221 and does not necessarily require thelaser beams to have the same burst or pulse duration. The assist laserbeam 211 may start before or during the process laser beam 221. Thelaser beams 211, 221 may also be directed to the workpiece 202 atdifferent times, for example, with the assist laser beam 211 before theprocess laser beam 221.

In the illustrated embodiment, the assist laser 210 may be arare-earth-doped fiber laser such as a GLP Series pulsed green fiberlaser available from IPG Photonics Corporation. In other embodiments,the assist laser 210 may include diode pumped solid state (DPSS) lasers,excimer lasers, gas lasers, and other types of lasers known to thoseskilled in the art. The process laser 220 may also be a rare-earth-dopedfiber laser such as a QCW Series single-mode ytterbium fiber laseravailable from IPG Photonics Corporation.

The assist laser beam delivery system 212 may include a variabletelescope to provide beam expansion and divergence control of the assistlaser beam 211. In particular, the divergence of the assist laser beam211 may be controlled to have an optimized numerical aperture (NA) tocreate substantially the same focal plane as the process laser beam 221after the laser beams 211, 221 are combined. The process laser beamdelivery system 222 may include a collimator such as, for example, acollimating lens with a focal length of 100 mm. Alternatively oradditionally, the beam delivery systems 212, 222 may also include otheroptics for modifying and/or directing the laser light to the desiredlocation. Such optics may include, without limitation, beam expanders,beam collimators, beam shaping lenses, reflectors, masks, beamsplittersand scanners (e.g., a galvanometer).

In the illustrated embodiment, the beam combiner 230 includes reflectorsor mirrors 232, 234 for selectively reflecting the wavelengths of theassist and process laser beams 211, 221, respectively, such that thebeams 211, 221 are directed along the same optical axis. The firstmirror 232 is coated to reflect the wavelength of the process laser beam221, and the second mirror 234 is coated on one side to reflect thewavelength of the process laser beam 221 and uncoated on the other sideto allow at least a portion of the assist laser beam 211 to passthrough. Thus, the second mirror 234 combines both beams 211, 221. In anembodiment with a green assist laser beam 211 and an IR process laserbeam 221, for example, the first mirror 232 may be IR coated and thesecond mirror 234 may be IR coated on one side and uncoated on the otherside. The uncoated side of the second mirror 234 may still reflect aportion of the assist laser beam 211 to a beam dump 250. Otherembodiments for the beam combiner 230 are also within the scope of thepresent disclosure.

The mirrors 252, 254, 256 may be coated to reflect the desiredwavelengths of the laser beams 211, 221. In an embodiment with a greenassist laser beam 211 and an IR process laser beam 221, for example, themirrors 252, 254 reflecting the green laser beam may be 532 nm or greencoated mirrors capable of reflecting the green assist laser beam 211 andthe mirror 256 may be a dual IR-green coated mirror capable ofreflecting both the green assist laser beam 211 and the IR process laserbeam 221. In one embodiment, the transmission of the multiple-beam laserprocessing system 200 may be 40% for the assist laser beam 211 and 90%for the process laser beam 221.

Although the illustrated embodiment shows free space delivery usingmirrors, other optical components may also be used to deliver and/orcombine the lasers. For example, one or more fibers may be used todeliver the laser beams to the laser processing head 260. In thisembodiment, the lasers may be combined by focusing the lasers to thesame location 208 on or within the workpiece 202.

The focus lens 240 may be a singlet focusing lens such as, for example,a lens with an 88 mm focal length and coated for IR. The focus lens 240may be capable of focusing the laser beams to a beam spot with adiameter or dimension in a range of about 30 to 40 μm. In otherembodiments, the beam delivery systems and focus lens 24 may be capableof focusing the lasers 211, 221 to an even smaller beam spot, forexample, as small as 15 μm or smaller.

In the illustrated embodiment, the laser processing head 260 includes agas assist nozzle 262 to direct a pressurized gaseous medium to theworkpiece 202 together with the laser beams to facilitate laserprocessing, for example, when using a thermal cutting process where thegas helps to expel molten material. The gaseous medium may include, forexample, oxygen (O₂). In other embodiments, the gaseous medium may be aninert gas, such as nitrogen, argon or helium.

Although the illustrated embodiments show multiple lasers 210, 220generating the assist laser beam 211 and the process laser beam 221, themultiple laser beam processing method may also be performed using thesame laser source to produce both the assist laser beam 211 and theprocess laser beam 221. For example, an assist laser beam may begenerated from a laser source with one set of parameters (e.g., ashorter wavelength and/or pulse duration) and a process laser beam maybe generated from the same laser source with a different set ofparameters (e.g., a longer wavelength and/or pulse duration). A singlelaser beam generated by a laser source may also be split and modifiedwith different beam delivery systems to produce the assist laser beamand the process laser beam with distinct characteristics.

The laser processing system 100 and the multiple-beam laser processingsystem 200 described above both may be used to perform cutting and/orpost-cut processing of hard dielectric materials as described herein. Inthe laser processing system 100, for example, the QCW laser 110 may beoperated with one set of parameters to generate a first laser beam forcutting and may be operated with another set of parameters (e.g., adifferent pulse duration, duty cycle, pulse energy, pulse repetitionrate, etc.) to generate a second laser beam for post-cut processing. Inthe multiple-beam laser processing system 200, one of the lasers 220 maybe used to generate a laser beam suitable for cutting the harddielectric material and the other of the lasers 210 may be used togenerate a laser beam suitable for post-cut processing the harddielectric material. Methods for post-cut processing are described ingreater detail below.

In the embodiment of the multiple-beam laser processing system 200 shownin FIG. 2, the multiple beams are directed at the workpiece along thesame optical axis or path using the same laser processing head 260.Referring to FIG. 3, another embodiment of a multiple-beam laserprocessing system 300 may direct multiple laser beams along differentoptical axes or paths. In this multiple-beam laser processing system300, different lasers requiring different optics may be used. Thismultiple-beam laser processing system 300 may also be used to performcutting and/or post-cut processing of hard dielectric materialsaccording to the methods described above and below.

The multiple-beam laser processing system 300 generally includes a firstlaser system 310 for generating and delivering a first laser beam 311and a second laser system 320 for generating and delivering a secondlaser beam 321. Each of the laser systems 310, 320 includes a beamdelivery system 312, 322 for delivering the respective first and secondlaser beams 311, 321 generated by respective first and second lasersources 314, 324. The beam delivery systems 312, 32 may be focused beam,shaped beam, scanned beam or thermal cutting head beam delivery systems.The beam delivery systems 312, 322 may include any combination of opticsor other elements used in such beam delivery systems including, withoutlimitation, beam expanders, beam collimators, beam shaping lenses,reflectors, masks, beamsplitters, focusing lenses, and scanners (e.g., agalvanometer).

The laser sources 314, 324 may include, without limitation, fiberlasers, diode-pumped solid state (DPSS) lasers, and excimer lasers. Inthe illustrated embodiment, at least the first laser source 314 is afiber laser that emits laser light from a fiber 315. The first lasersource 314 may include, for example, a QCW fiber laser such as the QCWIR single mode fiber laser described above. At least the first lasersystem 310 may also include a laser processing head 360 with a gasassist nozzle to direct a pressurized gaseous medium to the workpiece302 to facilitate laser processing, for example, as described above.

The second laser source 324 generates the second laser beam 321 withdifferent characteristics or parameters (e.g., wavelength, pulseduration, energy, power, orientation) than the first laser beam 311generated by the first laser system 310. The second laser source 324 mayinclude, for example, a fiber laser of a shorter wavelength (e.g.,green) than the first laser source 314 and/or a fiber laser of a shorterpulse duration (e.g., picoseconds or shorter) than the first lasersource 314. The second laser source 324 may also include an excimerlaser or a DPSS laser.

The second laser system 320 may also be configured to angle the secondlaser beam 321 relative to the surface of the workpiece 302. For abeveling or polishing operation, for example, the second laser beam 321may be angled with an angle of incidence that is greater than 0° andless than the critical angle and more preferably in a range of 15° to65° relative to an axis normal to the surface of the workpiece 302. Asused herein, “critical angle” refers to the angle of incidence abovewhich total reflection occurs. One way to angle a laser beam is bydirecting the laser beam off axis relative to a focal lens. Othertechniques for angling the laser may include reflecting the beam at anangle in the beam delivery system and tilting a laser processing head.With a fiber laser, for example, the fiber delivery may be provideddirectly to a laser processing head, which is moved like a multi axisrobot around the part. In other examples, the part may be moved inmultiple axes with the beam not moving.

The multiple-beam laser processing system 300 further includes at leastone motion stage 370 for supporting the workpiece 302 and moving theworkpiece 302 in one or more axes or directions relative to the firstlaser beam 311 and/or the second laser beam 321. The motion stage 370may include an X-Y theta motion stage capable of rotating the workpieceand moving the workpiece along the X and Y axes, such as the type knownto those skilled in the art and currently available. The motion stage370 may also be capable of tilting the workpiece 302 relative to a laserbeam, for example, instead of angling the laser beam. Although onemotion stage 370 is shown, the multiple-beam laser processing system 300may include a motion stage for each of the laser systems 310, 320 andthe workpiece 302 may be transferred from one motion stage to the otherfor processing by the different laser systems 310, 320. A control system372 may be used to control the motion stage 370 as well as the operationof the laser systems 310, 320. The control system 372 may include anycombination of hardware and software used for controlling lasermachining systems.

In at least one embodiment, the first laser system 310 is used forcutting hard dielectric materials and the second laser system 320 isused for post-cut processing a part cut from a hard dielectric material.The first laser source 314 may thus be a laser source suited to cuttinghard dielectric materials efficiently and with a relatively high speedsuch as a QCW IR laser as described above. The second laser source 324may be a laser source suited to beveling and/or polishing cut edges ofthe part cut from a hard dielectric material to reduce or remove edgedefects without inducing additional sub-surface stress. Thus, when thefirst laser system 310 cuts a part and creates edge defects such asstress concentrations, the second laser system 320 may be used to returnthe cut parts to a pre-cut stress condition. In general, laser beamsthat provide better absorption and coupling with the hard dielectricmaterial without significant thermal effects may be better suited forbeveling and/or polishing.

In some embodiments, the second laser source 324 may include a shorterwavelength laser, such as 193 nm or 248 nm excimer lasers, or a shorterpulse laser such as an ultrafast laser (e.g., a picosecond laser or afemtosecond laser). In transparent materials, the shorter wavelengthlasers provide better absorption because of the higher photon energy andthe shorter pulse lasers provide higher nonlinear absorption because ofthe higher peak power. Where the second laser source 324 is an ultrafastor picosecond laser, for example, the laser beam may be generated with awavelength in the IR range (e.g., 1060-1070 nm), the green range (e.g.,532 nm), or the UV range (e.g., 266 nm, 355 nm), with an energy densityin a range of about 5 to 15 J/cm² and with a pulse repetition rate ofgreater than 200 kHz. An ultrafast or picosecond laser may be directedat the workpiece with a high scanning speed galvo process. Where thesecond laser source 324 is an excimer laser, for example, the laser beammay be generated with a pulse duration in a range of 10 to 30 ns, withan energy density in a range of 10 to 20 J/cm², and a repetition rate ina range of 100 to 400 Hz. An excimer laser may be directed at theworkpiece with an imaging technique and stage-based process that movesthe workpiece relative to the laser beam. QCW lasers with goodfocusability (e.g., M2<1.05 for single mode) are also capable ofproviding higher power densities for coupling. Other lasers may also beused for the second laser source 324 including other fiber lasers orexcimer lasers in the UV range or the visible range and with other pulsedurations.

For any of the beveling and polishing operations described in greaterdetail below, the laser beam may be generated with parameters thatprovide the absorption sufficient to ablate and/or melt the material,depending upon the operation, without undesired thermal effects. Theprocess parameters of the laser may be adjusted differently forpolishing than for beveling. In a polishing operation, for example, alower energy density may be used to achieve a smaller removal rate perpulse and less affectation of surrounding material.

In other embodiments, at least one of the laser systems 310, 320 may beused to perform multiple processing operations. The first laser system310 may be used, for example, to cut a part from a hard dielectricmaterial and then to bevel the edges of the cut part and the secondlaser system 320 may be used to polish the beveled edges.

FIGS. 4A-4C show one method for polishing a cut edge 403 of a cut part402 cut from a hard dielectric material. As shown, the cut part 402includes edge defects 404, such as chipping and cracks, proximate thecut edge 403. These edge defects 404 may be a result of laser cuttingthe part 402 from a hard dielectric material, for example, using a QCWIR fiber laser. In this example, the cut edge 403 is substantiallyperpendicular to a surface 406 of the cut part 402 and the laser beam421 is directed substantially perpendicular or normal to the surface 406of the cut part 402. The laser beam 421 may be located at a depth 405(FIGS. 4A and 4B) sufficient to remove and/or modify (e.g., by ablationand/or melting) the material at the cut edge 403 such that the edgedefects 404 are removed or reduced. In one example, the depth 405 ofmaterial removal may be in a range of about 10-30 microns. The laserbeam 421 may be scanned along the edge 403 (e.g., by moving the beam 421and/or the cut part 402) to produce a polished edge 408 (FIG. 4C) alonga length of the part 402.

FIGS. 5A-5C show another method for polishing a beveled edge 503 of acut part 502 cut from a hard dielectric material. In this example, thebeveled edge 503 forms an angle relative to the surface 506 of the cutpart 502. The beveled edge 503 may be formed when the cut part 502 isfirst cut from a hard dielectric material by cutting with an angledbeam. The beveled edge 503 may also be formed after the cut part 502 isfirst cut with a straight or perpendicular cut and then beveled, forexample, using one of the beveling operations described below. Thebeveled edge 503 may thus include edge defects (not shown) resultingfrom the cut and/or a rough surface from the beveling operation. Thelaser beam 521 may be angled (e.g., shown with about a 60° angle ofincidence) to correspond approximately to the angle of the beveled edge503 and located at a depth 505 (FIGS. 5A and 5B) sufficient to removeand/or modify (e.g., by ablation and/or melting) the material at thebeveled edge 503 such that edge defects and/or surface roughness areremoved or reduced. In one example, the depth 505 of material removalmay be in a range of about 10-30 microns. The angled laser beam 521 maybe scanned along the beveled edge 503 (e.g., by moving the beam 521and/or the cut part 502) to produce a polished, beveled edge 508 (FIG.5C) along a length of the part 502.

FIGS. 6A-6D show one method for beveling an edge 603 of a cut part 602cut from a hard dielectric material. In this example, a straight laserbeam 621 is directed perpendicular or normal to a surface 606 of the cutpart 602 to remove a layer of material (e.g., by ablation) proximate theedge 603 by scanning the laser beam 621 along the edge 603 (e.g., bymoving the beam 621 and/or the cut part 602). After each layer ofmaterial is removed, the cut part 602 is moved away from the beam 621such that the laser beam 621 removes material to a greater depth closerto the edge 603, thereby laser milling the cut part to form a bevelededge 608. The beveled edge 608 may have a surface roughness, which maybe removed by laser polishing the beveled edge 608 as describe above.

FIGS. 7A-7D show another method for beveling an edge 703 of a cut part702 cut from a hard dielectric material. In this example, an angledlaser beam 721 (e.g., shown at about 45° angle of incidence) is used toremove angled layers of material (e.g., by ablation) proximate the edge703 by scanning the angled laser beam 721 along the edge 703 (e.g., bymoving the beam 721 and/or the cut part 702). After each angled layer ofmaterial is removed, the cut part 702 is moved toward the angled laserbeam 721 such that the angled laser beam 721 removes material to agreater depth at the edge 703, thereby laser milling the cut part toform a beveled edge 708.

FIGS. 8A and 8B show a further method for beveling an edge 803 of a cutpart 802 cut from a hard dielectric material. In this example, an angledlaser beam 821 is directed at an angle relative to a surface 806 of thecut part 802 and scanned along the edge 803 (e.g., by moving the beam821 and/or the cut part 802) to remove the edge 803 leaving a bevelededge 808.

Although the above techniques for beveling and polishing generallyinvolve the laser beam at a fixed angle relative to the edge beingbeveled or polished, various machining strategies may be used to controlthe angle of the laser beam. The angle of the laser beam may becontrolled, for example, to bevel a straight bevel at different angles.The orientation of an angled laser beam relative to the part may also becontrolled to change a cut angle within a range of angles to bevel arounded bevel as described below.

FIGS. 9A-9C illustrate one way to change a cut angle β by changing anorientation of an angled laser beam relative to the edge of the cut part902. The angled laser beam 921 a, 921 b (shown in FIG. 9A in twodifferent orientations aligned with different edges 903 a, 903 b) formsan angle β relative to a surface 906 of the cut part 902 (i.e., in aplane containing the laser beam and normal to the surface 906). The cutangle β is the angle of the cut edge surface relative to the surface 906of the part 902 as the angled laser beam moves relative to the part (seeFIG. 9B). By changing the orientation of the angled laser beam 921 a,921 b relative to the edges 903 a, 903 b of the cut part 902, the cutangle β may be changed while the laser angle α remains the same.

In this example, the change in orientation of the angled laser beam 921a, 921 b is coordinated with respect to the positioning of the part 902to produce different cut angles. When the angled laser beam 921 a isaligned with the X axis (and edge 903 a) as shown, the angled laser beam921 a would machine a straight side wall (i.e., a cut angle β of 90°) inthe edge 903 a of the part 902 when scanned along the X axis and wouldmachine an angled side wall or bevel (i.e., a cut angle β equal to thelaser angle α) in the edge 903 b of the part 902 when scanned along theY axis. When the angled laser beam 921 b is aligned with the Y axis (andedge 903 b) as shown, the angled laser beam 921 b would machine astraight side wall in the edge 903 b of the part 902 when scanned alongthe Y axis and would machine an angled side wall or bevel in the edge903 a of the part 902 when scanned along the X axis.

The orientation or alignment of the angled laser beam 921 a, 921 b maybe changed relative to the part 902 by rotating the angled laser beamand/or by rotating the part, which causes the angled laser beam 921 a,921 b to present different cut angles β relative to the edges 903 a, 903b of the part 902. When beveling a rectangular part 902 with a cut angleβ equal to the laser angle α, for example, the angled laser beam 921 aaligned with the X axis may be scanned along the Y axis to form astraight bevel on one edge 903 b and then the part and/or the beam maybe rotated 90° such that the angled laser beam 921 b aligned with the Yaxis may be scanned along the X axis to form a straight bevel on theadjacent edge 903 a.

As shown in FIG. 9B, the cut angle β may be varied within a range ofangles between 90° (when aligned with the scanning axis) and the laserangle α (when perpendicular to the scanning axis) by changing theorientation of the angled laser beam relative to the part 902 (e.g., byrotating the angled laser beam and/or by rotating the part). FIG. 9Bshows the angled laser beam 921 a aligned with the X axis (i.e., a cutangle β of 90°), the angled laser beam 921 b aligned with the Y axis(i.e., a cut angle β equal to the laser angle α), and the angled laserbeam 921 c at an intermediate alignment position (i.e., a cut angle βbetween 90° and the laser angle α). The part 902 may be moved withcoordinated motion in multiple axes to change the orientation of theangled laser beam relative to the part 902 and thus to change the cutangle β within this range of angles. Although the angled beam 921 c isshown at only one intermediate alignment position, the angled beam 921 cmay be moved to multiple intermediate alignment positions correspondingto different cut angles within the range of cut angles. The angled laserbeam 921 a-921 c may thus be scanned along the edge 903 b with differentorientations such that the angled laser beam provides a range of cutangles along the edge 903 b to form a rounded bevel 908, as shown inFIG. 9C.

FIGS. 10A and 10B show another method for changing the cut angle of alaser beam 1021 relative to a cut part 1002. In this example, the laserbeam 1021 is directed with an angle of incidence of 0° (e.g., 90°relative to the horizontal plane) and the cut part 1002 is moved awayfrom the horizontal plane to change the angle of the laser beam 1021relative to the part 1002 and thus the cut angle. The cut part 1002 maybe moved to provide a range of cut angles and the laser 1021 may bescanned along an edge 1003 to bevel at multiple cut angles to form arounded bevel 1008.

Referring to FIGS. 11A and 11B, an angled laser beam 1121 may also beused to bevel a circular part 1102. The angled laser beam forms an angleα relative to a surface 1106 of the circular part 1102, but the cutangle may be changed without changing the angle β by changing theorientation of the circular part 1102 relative to the angled laser beam1121. Where the angled laser beam 1121 is aligned with the radius of thecircular part 1102 (FIG. 11A), for example, the angled laser beam 1121will cut a beveled edge with a cut angle corresponding to the angle α.Where the angled beam 1121 is moved to a different position at a beamangle δ relative to the radius, the angled beam 1121 will cut a bevelededge at some cut angle greater than the angle α. When the angled beam1121 a is at a beam angle of 90°, the angled beam 1121 a cuts the edge1103 normal to the surface 1106 of the part 1102 (i.e., a cut angle of90°). Thus, the orientation of the circular part 1102 may be changed tochange the alignment of the angled laser beam 1121 and thus to changethe cut angle.

As shown in FIGS. 12A and 12B, the circular part 1102 may be moved withcoordinated motion in multiple axes to bevel the circular edge 1103 ofthe part. In one example, the circular part 1102 may be moved with agenerally circular motion (as indicated by arrow 1101) by moving themotion stage in the X and Y directions while also rotating the thetaaxis with an equal and opposite angular velocity. FIG. 12A shows theangled beam 1121 aligned with the radius (i.e., a beam angle of 0°) toprovide a cut angle corresponding the angle α. FIG. 12B shows the angledbeam 1121 offset from the radius (i.e., with a beam angle of δ) toprovide a cut angle greater than the angle α. As shown in FIG. 13, theorientation of the circular part may be changed within a range of beamangles (referred to as the include angle) such that the circular part iscut at a range of cut angles, for example, to provide a rounded bevel.FIG. 14 shows a circular part with a straight beveled edge and FIG. 15shows a circular part with a rounded beveled edge.

Accordingly, laser processing systems and methods, as described herein,are capable of efficiently laser cutting hard dielectric materials atincreased speeds in a time-effective and a cost-effective manner whilealso reducing edge defects. Although the exemplary embodiments describepost-cut processing of a cut part, the methods for beveling andpolishing described herein may be used on edges of any part.

While the principles of the invention have been described herein, it isto be understood by those skilled in the art that this description ismade only by way of example and not as a limitation as to the scope ofthe invention. Other embodiments are contemplated within the scope ofthe present invention in addition to the example embodiments shown anddescribed herein. Modifications and substitutions by one of ordinaryskill in the art are considered to be within the scope of the presentinvention, which is not to be limited except by the following claims.

What is claimed is:
 1. A method for laser cutting and post-cutprocessing a part from a hard dielectric material, the methodcomprising: cutting at least one part from a hard dielectric materialusing at least a first laser beam, wherein the first laser beam isemitted from a continuous wave laser operating in a quasi-continuouswave (“QCW”) mode so as to emit consecutive pulses of laser light at awavelength ranging between about 1060 nm and about 1070 nm; and post-cutprocessing cut edges of the at least one part using at least a secondlaser beam to bevel and/or polish the cut edges of the at least one partsuch that edge defects are reduced.
 2. The method of claim 1 wherein thesecond laser beam is emitted from the continuous wave laser operating inthe QCW mode.
 3. The method of claim 1 wherein the second laser beamforms an angle of incidence relative to a surface of the cut part,wherein the angle of incidence is greater than 0°.
 4. The method ofclaim 1 wherein the second laser beam forms an angle of incidencerelative to a surface of the cut part, wherein the angle of incidence isin the range of 15° to 45°.
 5. The method of claim 1 wherein the secondlaser beam forms an angle of incidence relative to a surface of the cutpart, wherein the angle of incidence is greater than 0°, and whereinpost-cut processing cut edges of the at least one part includes movingthe cut part with coordinated motion in multiple axes relative to thesecond laser beam to bevel the cut edges.
 6. The method of claim 1wherein post-cut processing with the second laser beam bevels the cutedge to form a flat edge that is not perpendicular to a surface of thepart.
 7. The method of claim 1 wherein post-cut processing with thesecond laser beam bevels the cut edge to form a rounded edge that is notperpendicular to a surface of the part.
 8. The method of claim 1 whereinthe second laser beam is emitted from a second laser, wherein the secondlaser emits laser light at a shorter wavelength and/or a shorter pulsewidth than the first laser.
 9. The method of claim 8 wherein the secondlaser is an excimer laser having a wavelength of 193 nm or 248 nm. 10.The method of claim 8 wherein the second laser is an ultrafast laserhaving a wavelength in the IR range, the green range or the UV range.11. The method of claim 1 wherein the continuous wave laser operating inQCW mode is a single mode (SM) fiber laser.
 12. The method of claim 1wherein the continuous wave laser operating in QCW mode is operated witha duty cycle ranging between about 1% and about 15%.
 13. The method ofclaim 1 wherein the continuous wave laser operating in QCW mode isoperated with a pulse width ranging between about 10 microseconds andabout 600 microseconds.
 14. The method of claim 1 wherein the cutting isassisted by a gas supplied to the part with the first laser beam.